How can I monitor disk io?

Have a look at iotop:

Total DISK READ :       0.00 B/s | Total DISK WRITE :       0.00 B/s
Actual DISK READ:       0.00 B/s | Actual DISK WRITE:       0.00 B/s
  TID  PRIO  USER     DISK READ  DISK WRITE  SWAPIN     IO>    COMMAND                                                                                                             
    1 be/4 root        0.00 B/s    0.00 B/s  0.00 %  0.00 % init splash
    2 be/4 root        0.00 B/s    0.00 B/s  0.00 %  0.00 % [kthreadd]
    4 be/0 root        0.00 B/s    0.00 B/s  0.00 %  0.00 % [kworker/0:0H]
    6 be/0 root        0.00 B/s    0.00 B/s  0.00 %  0.00 % [mm_percpu_wq]
    7 be/4 root        0.00 B/s    0.00 B/s  0.00 %  0.00 % [ksoftirqd/0]
    8 be/4 root        0.00 B/s    0.00 B/s  0.00 %  0.00 % [rcu_sched]

Or iodump, if that’s more down your way of thinking.

Note: This requires at least kernel 2.6.20 to work.

I like dstat. It can show totals and statistics per disk and even md-devices (RAID), also can use colors for better overview:

$ dstat -tdD total,sda,sdb,sdc,md1 60 
----system---- -dsk/total----dsk/sda-----dsk/sdb-----dsk/sdc-----dsk/md1--
     time     | read  writ: read  writ: read  writ: read  writ: read  writ
08-11 22:08:17|3549k  277k: 144k   28k: 851k   62k: 852k   60k:  25k   82k
08-11 22:09:17|  60k  258k:1775B   15k:  13k   63k:  15k   60k:  68B   74k
08-11 22:10:17| 176k  499k:   0    14k:  41k  122k:  41k  125k: 273B  157k
08-11 22:11:17|  42k  230k:   0    14k:9830B   54k:  14k   51k:   0    70k
08-11 22:11:52|  28k  132k:   0  5032B:5266B   33k:9479B   28k:   0    37k

• -t for timestamps
• -d for disk statistics
• -D to specify the exact devices to report

• 60 to average over 60 seconds. The display is updated every second, but only once per 60 seconds a new line will be started.

• not used in this example, but -c can report wait IO percentage, which in most cases is related to the CPU waiting for data from the disks.

It is available for most Linux distributions, but sometimes needs to be installed from repositories.

Just from files on your computer (assuming a recent kernel) you can ask /sys/block/sda/stat (documented at kernel.org) or /proc/diskstats. It will need some translating, however. But it’s nice for a quick and dirty check.

The best thing to do if you want to see performance on a long period is to use Centreon
which is a powerful tools build on Nagios. Centreon make you able to monitor by drawing graphs of resource’s performances and lot of other things.

Monitoring Disk Io can be done by multiple tools like the following.

1. Iostat
2. Iozone
3. SAR
4. vmstat

Also some important operating system concepts are very much necessary to comprehend them..read the Linux IO complete tutorial

Another option is to use: sudo iotop -aoP

-a    Will show accumulated output
-o    Will only output 
-P    Will only show processes instead of threads

This program will tell you how much a process has written to disk and read from disk since iotop was started.

Another great tool for a quick overview where the load comes from is atop

It can show you an overview over all resources (CPU, memory/swap, network and disk I/O) or you can drill down to a single resource and sort processes by how much they consume.

Why not try nmon. It does disks and network with processes. Originally for AIX but it has been ported to Linux for some years now.

I am the author of diskgraph which is a command line tool that plots the disk IO in a terminal. You select which disk, as an argument on the command-line, like sda or nvme0n1.

$ ./diskgraph nvme0n1

In red: the write bandwidth

In green: the read bandwidth

In orange: the number of IO operations that are in-flight.

Please note that this utility depends on features introduced in Linux 5. In other words, it will not work with Linux 4 or earlier.

If you use zfs, then there is a built in tool for this:

% zpool iostat -T d -n -H -v 1 | head -5
Sat Dec 24 23:09:49 2022
datatank    24.8T   31.6T   39  70  5.76M   4.55M
mirror-0    4.29T   4.80T   3   9   802K    765K
gpt/slot_A1 -   -   2   4   511K    403K
gpt/slot_B7 -   -   1   4   335K    405K

• The -T d option puts the date lines (e.g Dec 24).
• The -H enables scripted mode by omitting headers and making the data well formed.
• The -v enables statistics for each individual vdev in the pool.
• Finally the 1 is how many seconds to wait for the next update.
• The head -5 is just to demonstrate you can pipe the output.